1. Field of the Invention
This invention relates to energy concentrators, and, more particularly, to low-cost concentrators for concentration of solar energy.
2. Description of the Prior Art
While solar energy can be collected and transformed into a useful energy form without concentration, it is well-known that the value of the energy or the cost of the collecting system, or both, can be improved by means of optical concentration. For example, in solar thermal collectors, optical concentration results in higher temperatures and lower thermal losses; in photovoltaic collectors, optical concentration reduces the number of expensive solar cells required for a given energy output. Many types of optical concentrators for solar energy applications have been discussed in the literature.
For the purposes of this discussion, optical concentrators for solar energy can be divided into two classes: single-axis (line focusing) and two-axis (point focusing). Single-axis concentrators, such as parabolic troughs and linear Fresnel reflectors and lenses, are less expensive but are limited in attainable concentration ratio. Also, the line focus requires an absorber for the concentrated solar energy in the form of a linear strip, which is inconvenient for photovoltaic absorbers, since solar cells are most readily produced in a circular shape. Two-axis concentrators do not have these disadvantages, but they are more expensive to produce and also require tracking of the sun in two axes, which requires an expensive and complex gimbal mount.
Thus, there is a need for a two-axis optical concentrator for solar energy systems which would achieve concentration ratios higher than can feasibly be obtained from a single-axis optical concentrator, yet would not be substantially more expensive to fabricate. This invention meets this need, and in addition can be designed so that the concentration ratios in the two axes are unequal, if desired. In many cases, this allows considerable savings in the design of the tracking mount, so that a two-axis concentrating solar collector can be fabricated at only slightly higher cost than a single-axis unit.